* lisp/isearch.el (lazy-highlight-buffer): New defcustom. (Bug#29360)

* lisp/isearch.el (lazy-highlight-buffer): New defcustom.  (Bug#29360)

(lazy-highlight-buffer-max-at-a-time): New defcustom.
(isearch-lazy-highlight-buffer): New defvar.
(isearch-lazy-highlight-new-loop): Don't check changes in window
boundaries when lazy-highlight-buffer is non-nil.
Move code that extends start/end to match whole string at point
here from isearch-lazy-highlight-search.
(isearch-lazy-highlight-search): Add args string and bound
like in other search functions.  Move calculation of bound
to isearch-lazy-highlight-update.
(isearch-lazy-highlight-match): New function with code extracted from
isearch-lazy-highlight-update to be called also from
isearch-lazy-highlight-buffer-update.
(isearch-lazy-highlight-update): Reuse the values returned from
window-group-start and window-group-end.  At the end schedule the
timer to call isearch-lazy-highlight-buffer-update when
isearch-lazy-highlight-buffer is non-nil.
(isearch-lazy-highlight-buffer-update): New function.